Electrodeless fluorescent lamps generally require mounting in a special fixture designed to shield the surrounding area from the EMI generated by the operation of the lamp. Such fixtures function as a Faraday shield and allow the lamp to operate without too much disturbance to adjacent devices; however, such special fixtures also limit the places where the lamps can be employed.
Several current lamps attempt to solve this problem by various means, one of which involves applying EMI screening to the lamp envelope in the form of a transparent conductive coating on the interior surface of the lens portion of the lamp together with an opaque metal coating on the outside surfaces of the sides of the lamp envelope. The coatings are connected electrically to the local ground of the lamp. This system greatly increases the cost of the lamp and reduces the lamps efficiency and is really only suitable for PAR lamps.
Another approach, shown in U.S. Pat. No. 4,710,678, involves the use of a second winding interspersed between the primary windings on the ferrite core of the lamp. The second winding has one free end and the other end connected to one end of the primary winding. Interference currents at the supply mains with this approach are alleged to be strongly suppressed.
It would be an advance in the art if the EMI of electrodeless fluorescent lamps could be further improved at reasonable cost to allow more usage in residential and commercial applications.